When use getOne and findOne methods Spring Data JPA

Question

I have an use case where it calls the following   Override  Transactional propagation Propagation REQUIRES NEW  public UserControl getUserControlById Integer id       return this userControlRepository getOne id      Observe the  Transactional has Propagation REQUIRES NEW and the repository uses getOne  When I run the app  I receive the following error message  Exception in thread  quot main quot  org hibernate LazyInitializationException   could not initialize proxy - no Session      But If I change the getOne id  by findOne id  all works fine  BTW  just before the use case calls the getUserControlById method  it already has called the insertUserControl method  Override  Transactional propagation Propagation REQUIRES NEW  public UserControl insertUserControl UserControl userControl        return this userControlRepository save userControl      Both methods are Propagation REQUIRES NEW because I am doing a simple audit control  I use the getOne method because it is defined in the JpaRepository interface and my Repository interface extends from there  I am working with JPA of course  The JpaRepository interface extends from CrudRepository  The findOne id  method is defined in CrudRepository  My questions are   Why fail the getOne id  method  When I should use the getOne id  method   I am working with other repositories and all use the getOne id  method and all work fine  only when I use the Propagation REQUIRES NEW it fails  According with the getOne API   Returns a reference to the entity with the given identifier   According with the findOne API   Retrieves an entity by its id    When I should use the findOne id  method   What method is recommended to be used

User · Answer

1  Why does the getOne id  method fail   See this section in the docs  You overriding the already in place transaction might be causing the issue  However  without more info this one is difficult to answer   2  When I should use the getOne id  method   Without digging into the internals of Spring Data JPA  the difference seems to be in the mechanism used to retrieve the entity   If you look at the JavaDoc for getOne ID  under See Also   See Also  EntityManager getReference Class  Object    it seems that this method just delegates to the JPA entity manager s implementation   However  the docs for findOne ID  do not mention this   The clue is also in the names of the repositories  JpaRepository is JPA specific and therefore can delegate calls to the entity manager if so needed  CrudRepository is agnostic of the persistence technology used  Look here  It s used as a marker interface for multiple persistence technologies like JPA  Neo4J etc   So there s not really a  difference  in the two methods for your use cases  it s just that findOne ID  is more generic than the more specialised getOne ID   Which one you use is up to you and your project but I would personally stick to the findOne ID  as it makes your code less implementation specific and opens the doors to move to things like MongoDB etc  in the future without too much refactoring

User · Answer

The basic difference is that getOne is lazy loaded and findOne is not   Consider the following example   public static String NON EXISTING ID   -1      MyEntity getEnt   myEntityRepository getOne NON EXISTING ID   MyEntity findEnt   myEntityRepository findOne NON EXISTING ID    if findEnt    null         findEnt getText       findEnt is null - this code is not executed    if getEnt    null         getEnt getText       Throws exception - no data found  BUT getEnt is not null

User · Answer

TL DR  T findOne ID id   name in the old API    Optional lt T gt  findById ID id   name in the new API  relies on EntityManager find   that performs an entity eager loading   T getOne ID id  relies on EntityManager getReference   that performs an entity lazy loading  So to ensure the effective loading of the entity  invoking a method on it is required   findOne   findById   is really more clear and simple to use than getOne    So in the very most of cases  favor findOne   findById   over getOne       API Change  From at least  the 2 0 version  Spring-Data-Jpa modified findOne    Previously  it was defined in the CrudRepository interface as    T findOne ID primaryKey     Now  the single findOne   method that you will find in CrudRepository is which one defined in the QueryByExampleExecutor interface as     lt S extends T gt  Optional lt S gt  findOne Example lt S gt  example     That is implemented finally by SimpleJpaRepository  the default implementation of the CrudRepository interface  This method is a query by example search and you don t want to that as replacement      In fact  the method with the same behavior is still there in the new API but the method name has changed  It was renamed from findOne   to findById   in the CrudRepository interface    Optional lt T gt  findById ID id      Now it returns an Optional  Which is not so bad to prevent NullPointerException   So  the actual choice is now between Optional lt T gt  findById ID id  and T getOne ID id        Two distinct methods that rely on two distinct JPA EntityManager retrieval methods  1  The Optional lt T gt  findById ID id  javadoc states that it       Retrieves an entity by its id    As we look into the implementation  we can see that it relies on EntityManager find   to do the retrieval    public Optional lt T gt  findById ID id         Assert notNull id  ID MUST NOT BE NULL        Class lt T gt  domainType   getDomainClass         if  metadata    null            return Optional ofNullable em find domainType  id               LockModeType type   metadata getLockModeType         Map lt String  Object gt  hints   getQueryHints   withFetchGraphs em  asMap         return Optional ofNullable type    null   em find domainType  id  hints    em find domainType  id  type  hints        And here em find   is an EntityManager method declared as    public  lt T gt  T find Class lt T gt  entityClass  Object primaryKey                    Map lt String  Object gt  properties     Its javadoc states       Find by primary key  using the specified properties   So  retrieving a loaded entity seems expected     2  While the T getOne ID id  javadoc states  emphasis is mine        Returns a reference to the entity with the given identifier    In fact  the reference terminology is really board and JPA API doesn t specify any getOne   method  So the best thing to do to understand what the Spring wrapper does is looking into the implementation     Override public T getOne ID id        Assert notNull id  ID MUST NOT BE NULL       return em getReference getDomainClass    id       Here em getReference   is an EntityManager method declared as    public  lt T gt  T getReference Class lt T gt  entityClass                                Object primaryKey     And fortunately  the EntityManager javadoc defined better its intention  emphasis is mine        Get an instance  whose state may be lazily fetched  If the requested   instance does not exist in the database  the EntityNotFoundException   is thrown when the instance state is first accessed   The persistence   provider runtime is permitted to throw the EntityNotFoundException   when getReference is called   The application should not expect that   the instance state will be available upon detachment  unless it was   accessed by the application while the entity manager was open    So  invoking getOne   may return a lazily fetched entity  Here  the lazy fetching doesn t refer to relationships of the entity but the entity itself     It means that if we invoke getOne   and then the Persistence context is closed  the entity may be never loaded and so the result is really unpredictable  For example if the proxy object is serialized  you could get a null reference as serialized result or if a method is invoked on the proxy object  an exception such as LazyInitializationException is thrown  So in this kind of situation  the throw of EntityNotFoundException that is the main reason to use getOne   to handle an instance that does not exist in the database as an error situation may be never performed while the entity is not existing   In any case  to ensure its loading you have to manipulate the entity while the session is opened  You can do it by invoking any method on the entity  Or a better alternative use findById ID id  instead of     Why a so unclear API    To finish  two questions for Spring-Data-JPA developers    why not having a clearer documentation for getOne      Entity lazy loading is really not a detail  why do you need to introduce getOne   to wrap EM getReference     Why not simply stick to the wrapped method  getReference     This EM method is really very particular while getOne    conveys a so simple processing

User · Answer

I had a similar problem understanding why JpaRespository getOne id  does not work and throw an error    I went and change to JpaRespository findById id  which requires you to return an Optional    This is probably my first comment on StackOverflow

User · Answer

I really find very difficult from the above answers   From debugging perspective i almost spent 8 hours to know the silly mistake   I have testing spring hibernate dozer Mysql project  To be clear   I have User entity  Book Entity  You do the calculations of mapping   Were the Multiple books tied to One user  But in UserServiceImpl i was trying to find it by getOne userId    public UserDTO getById int userId  throws Exception        final User user   userDao getOne userId        if  user    null            throw new ServiceException  User not found   HttpStatus NOT FOUND             userDto   mapEntityToDto transformBO user  UserDTO class        return userDto      The Rest result is      collection          version    1 0        data              id   1           name    TEST ME            bookList   null             error   null       statusCode   200     booleanStatus   null      The above code did not fetch the books which is read by the user let say   The bookList was always null because of getOne ID   After changing to findOne ID   The result is      collection          version    1 0        data              id   0           name    Annama            bookList                                    id   2                   book no    The karma of searching                                       error   null       statusCode   200     booleanStatus   null

User · Answer

while spring jpa open-in-view was true  I didn t have any problem with getOne but after  setting it to false   i got LazyInitializationException  Then problem was solved by replacing with findById  Although there is another solution without replacing the getOne method  and that is put  Transactional at method which is calling repository getOne id   In this way transaction will exists and session will not be closed in your method and while using entity  there would not be any LazyInitializationException

User · Answer

The getOne methods returns only the reference from DB  lazy loading   So basically you are outside the transaction  the Transactional you have been declare in service class is not considered   and the error occur

[jpa] When use getOne and findOne methods Spring Data JPA

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